Why is this huge?
The differences between domestic rates and non-domestic rates are what kept the European Telecoms market from becoming truly European. As a German, the only viable option if I am spending most my time within Germany was to go with a German carrier. Now with the removal of roaming charges, the EU becomes the domestic market and in principle I could shop around other EU countries to find the best deal. Austria for example has some really good deals, so maybe I will go with a carrier from there. And with SEPA even billing should not be an issue.
The other (intended) thing this will spur is further consolidation of the EU Telecoms market as there will suddenly be a much larger number of competing players on the market. As I said, in principle Austrian Telecoms are now for the first time directly competing for customers with Spanish Telecoms in Germany, so I guess we'll see a lot more mergers in the close future. Which might turn out to be anticompetitive in the long run, mind.
(I blogged about it here [1] in more detail and with a few more resources, in case anyone is interested. Happy to explore this further with anyone into this topic)
[1] http://sveme.org/removing-eu-roaming-charges-is-a-big-deal.h...